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ISO Containers Earthing & Bonding - TNCS (PNB) Supply

Former Community Member
Former Community Member
I have a project to provide a 63A TP supply terminating with a Type B DB within an ISO container. Final circuits from the DB will supply industrial sockets located in the ISO via RCBO's and an external fan.

The ISO container is located on several concrete pads and internally is fully (wooden) boarded out.

The supply is TNCS PNB.

My current proposals are for a connection via a SWA supply cable (4c) and separate CPC, fed via a 63A Type C MCB.

The CPC will terminate onto a EMT.

The ISO container will have a main protective bonding conductor to the EMT using finely stranded cable. In addition bonding via flexible 'straps' will be provided to the doors.

I have not allowed to TT the installation due to the PNB supply.


Looking for advice on whether a local earth rod or ring earth electrode is the best option to earth the container locally and also the resistance figure to achieve.


Thanks Mike

 


 

Parents
  • 0
    Will the container really be a 'mobile or transportable unit' as far as the wiring is concerned? E.g. is it likely to be moved elsewhere and just hooked up to another supply? If not, and the container is being treated more like a of  bit pre-fab building which is intended to remain in the same place indefinitely then it might make more sense to treat it more like an ordinary installation - e,g. no need for finely stranded conductors.


    PME would still be a point to consider though. As Graham suggested, PNB isn't usually really TN-C-S (but can be in some rare circumstances - e,g. where the Tx serves more than one customer) and by definition isn't PME (as there's no requirement for multiple earthing), but for safety we usually regard all UK DNO earthing facilities as 'potentially PME' in case the DNO change the arrangement at a later date. Creating a TT island for the unit(s) is an obvious answer, but can cause difficulties where they're within reach or are connected to metalwork that's connected to the main installation.


       - Andy.
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  • 0
    Will the container really be a 'mobile or transportable unit' as far as the wiring is concerned? E.g. is it likely to be moved elsewhere and just hooked up to another supply? If not, and the container is being treated more like a of  bit pre-fab building which is intended to remain in the same place indefinitely then it might make more sense to treat it more like an ordinary installation - e,g. no need for finely stranded conductors.


    PME would still be a point to consider though. As Graham suggested, PNB isn't usually really TN-C-S (but can be in some rare circumstances - e,g. where the Tx serves more than one customer) and by definition isn't PME (as there's no requirement for multiple earthing), but for safety we usually regard all UK DNO earthing facilities as 'potentially PME' in case the DNO change the arrangement at a later date. Creating a TT island for the unit(s) is an obvious answer, but can cause difficulties where they're within reach or are connected to metalwork that's connected to the main installation.


       - Andy.
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